[Myocardial excitability under the influence of digitalis glycosides and anti-arrhythmia agent].

Using the technical procedure of transvenous cardiac pacing right ventricular myocardium was stimulated with various pulse duration (voltage-duration curves) and with paired stimuli utilizing double pacing technique, to determine diastolic threshold profile up to the absolute refractory period. Two kinds of cardiac drugs were tested: Digitalis glycosides increase distolic excitability and shorten refractory period. Anitarrhythmic drugs have different effects: Lidocaine and Phenytoine in several cases decrease slightly the stimulatory threshold and can shorten the refractory period. Procainamide and Ajmaline prolong the refractory period and increase the stimulatory threshold. Propranolol and Verapamil have no significant effect. Their major action is supraventricular. The results are important in view of clinical pharmacology of cardiac drugs and of long term cardiac pacemaker therapy.